1. Field of the Invention
The present invention relates to a positive photoresist composition having satisfactory sensitivity, definition, and depth of focus (DOF) properties. Particularly, the present invention relates to a positive photoresist composition which can form both dense patterns and isolation patterns with good shapes in the formation of mixed resist patterns including dense patterns and isolation patterns, and can minimize inverted taper shape formation of isolation resist patterns induced by shifts of focal depth to the minus side.
2. Description of the Related Art
In the manufacture of ultralarge-scale integrated circuits (Ultra LSI) where high definition of not more than half a micron, in particular, not more than 0.35 .mu.m is required, demands have been made on photoresist compositions which can form a resist pattern satisfactory in sensitivity, definition, and depth of focus (DOF) properties and having a good shape.
Separately, the manufacture of a highly value-added logic integrated circuit (logic IC) has received attention in recent years. Such a logic IC has a complicated wiring pattern. Specifically, the wiring pattern of the logic IC includes large portions of irregularly formed line-and-space (hereinafter referred to as "L&S"). In contrast, a dynamic random access memory (DRAM) chip includes large portions of regularly formed L&S.
In a photolithographic process using a photoresist composition, demands have been made to form a resist pattern having a good pattern shape not only in regions where L&S is regularly formed, i.e., dense pattern regions, but also in regions where L&S is irregularly formed, i.e., isolation pattern regions.
However, in the formation of an ultrafine resist pattern of not more than half a micrometer, particularly of not more than 0.35 .mu.m, resist patterns having good shapes both in dense patterns and isolation patterns are difficult to form. Specifically, if exposure conditions are changed to yield rectangular dense patterns with good shapes, the shapes of isolation patterns are deteriorated, and, in contrast, if exposure conditions are changed to yield rectangular isolation patterns with good shapes, the shapes of dense patterns are deteriorated.
Accordingly, mixed resist patterns with good shapes including both dense patterns and isolation patterns are difficult to form concurrently.
In addition, positive photoresist compositions are liable to invite inverted taper shapes of isolation patterns, which is caused by shifts of focal depth to the minus side, and are liable to induce pattern twist, and have deteriorated depth of focus (DOF) properties in isolation patterns.
Japanese Patent Laid-Open No. 2-296249 (conventional technique 1) describes a positive photoresist composition including, as a photosensitizer, a quinonediazidesulfonyl ester of a compound of the following formula: ##STR2##
wherein each of R.sup.1 to R.sup.5 is hydrogen, halogen, a C.sub.1 -C.sub.4 alkyl group, an alkenyl group, an alkoxy group or a hydroxyl group, where at least one is a group of the following formula: ##STR3##
wherein each of R.sup.6 and R.sup.7 is halogen, an alkyl group, or an alkenyl group, and n is 0, 1, or 2.
Compounds of the formula (I) for use in the invention as described below are included in compounds of the above general formula, but the conventional technique 1 lacks specific descriptions of the structures of the compounds of the formula (I).
With the photoresist composition exemplified in conventional technique 1 it is difficult to form either dense patterns or isolation patterns with good shapes in the formation of mixed resist patterns. In particular, this photoresist composition cannot effectively minimize inverted taper shape formation of isolation resist patterns induced by shifts of focal depth to the minus side.
Japanese Patent Laid-Open No. 5-323597 (conventional technique 2) describes a positive photoresist composition including, as a photosensitizer, a quinonediazidesulfonyl diester of a compound of the following formula: ##STR4##
or ##STR5##
wherein each of R.sub.1 and R.sub.2 is independently a hydrogen or halogen atom, --OCOR.sub.3, or an alkyl or alkoxy group which may be substituted, R.sub.3 is an alkyl or phenyl group which may be substituted, each of x and y is independently an integer of 1 to 3, and each of R, R.sub.0, R', and R.sub.0 ' is independently a hydrogen atom, an alkyl or phenyl group.
Compounds of the formula (I) for use in the invention as described below are included in compounds of the above general formula, but the conventional technique 2 lacks specific descriptions of the structures of the compounds of the formula (I).
With the photoresist composition exemplified in conventional technique 2 it is difficult to form either dense patterns or isolation patterns with good shapes in the formation of mixed resist patterns. In particular, this photoresist composition cannot effectively minimize inverted taper shape formation of isolation resist patterns induced by shifts of focal depth to the minus side.